1. Field of the Invention
The present invention relates to a gas turbine having a first compressor, a combustion chamber and a first turbine, The turbine is adapted to drive the compressor via a first shaft. The gas turbine is adapted for compression of the gas in the compressor, heating of the compressed gas in the combustion chamber and expansion of the heated gas in the turbine. The invention also relates to a method for engine-braking such a gas turbine.
2. Background
Gas turbines are used as, for example, engines for vehicles and aircraft, and as power plants in vessels, and in power stations for electricity production.
The gas turbine will be described below in a case in which it includes a free power turbine. This is a preferred, but in no way limiting application of the invention. The arrangement of the compressor, the turbine for driving the compressor via the first shaft, and the combustion chamber is usually referred to as a gas generator. The power turbine connected to a drive shaft is arranged downstream of the first turbine and is adapted to be driven by the gas from the first turbine. In other words, the gas generator and the power turbine are connected only by the expanded hot gases.
The gas turbine is preferably of the recuperative or regenerative type; that is to say, it includes a heat exchanger which is adapted to recover energy from the hot exhaust gases.
With their great power in relation to their weight, gas turbines are very suitable for the propulsion of vehicles, and this applies in particular to gas turbines with two shafts, one of which connects the free power turbine, via a vehicle transmission, to a driving shaft of the vehicle. One problem in vehicle applications is bringing about an engine-braking function. This applies in particular in the case of heavy-duty vehicles such as trucks. The present invention will be described below in a setting and situation in which it is applied in a vehicle for the propulsion thereof. This is a preferred, but in no way limiting application of the invention.
In gas turbines with a compressor driven by a turbine and a combustion chamber arranged therebetween, it is known to reduce, or shut off completely, the fuel supply to the combustion chamber for the purpose of reducing/braking the speed of the engine. In one respect, this method for speed reduction/engine-braking is relatively slow due to the fact that internal friction in gas turbines is very low and in another respect because of the fact that a relatively large part of the work performed in compression, in the compressor, is recovered when the subsequent expansion in the turbine takes place.